"The defacement was caught in minutes and corrected immediately," said Saara Bergstrom, a spokeswoman of the Finnish company. "The end-user data was in no risk at any point."
Reports earlier this week said that documents leaked by former National Security Agency contractor Edward Snowden suggested the NSA and Britain's GCHQ had been able to extract information through numerous smartphone apps, including Google Maps and the Angry Birds game franchise.
Rovio denied the claims, saying it does not "share data, collaborate or collude" with any spy agencies and that it would strive to ensure that user privacy is protected.
Rovio CEO Mikael Hed said the personal details of customers could have been accessed from information gathered by third-party advertising agencies.
"In order to protect our end users, we will, like all other companies using third-party advertising networks, have to re-evaluate working with these networks if they are being used for spying purposes," he said.
Angry Birds, an addictive birds-versus-pigs game that has been downloaded more than 1.7 billion times worldwide, is one of the latest examples of how everyday pieces of software can be turned into instruments of espionage. According to The New York Times and ProPublica, a U.S.-based nonprofit journalism group, a 2012 British intelligence report demonstrated how to extract Angry Bird users' information from phones running the Android operating system.
Another document listed other mobile apps, including those made by social networking giant Facebook, photo-sharing site Flickr, and the film-oriented Flixster.
Mikko Hypponen, from F-Secure computer security company, said the hacking into Rovio's website was a "good lesson" for mobile companies and app providers to make sure they protect customer privacy.
"There really is no reason why third-party advertising networks do not encrypt personal information on the Web. It's not rocket science," Hypponen said. "There will be a lot of pressure on these agencies."